Enhance Activitybar layout and item separation

[Lee Murray (mrleemurray)]

The Activity Bar hid view containers behind the "Additional Views" overflow menu while there was still room to show them. This was most visible with the compact Activity Bar and with Modern UI enabled, where it could collapse down to a single icon in a window that comfortably fits all of them.

Changes

• Size the overflow computation from the current item height instead of a hardcoded 52px, which did not track the compact Activity Bar (28px) or Modern UI (36px + 8px gap) sizes.
• Publish the Modern UI inter-item gap from TypeScript as --activity-bar-action-gap and consume it in floatingPanels.css, so the rendered spacing and the overflow computation share a single source of truth rather than restating the same value in both places.
• Reserve the measured height of the global Accounts/Manage icons rather than deriving it from the overflow action size, which over-reserved by one gap. GlobalCompositeBar.size() has no remaining callers and is removed.
• Give back the one leading-item gap that the per-item stride folds into every item, since the gap only renders between items — without it the last item still overflowed a gap early.
• Add regression coverage for the per-item stride, the published CSS variable, and the leading-gap compensation across all four size combinations.

Validation

• 21 ActivitybarPart unit tests pass.
• typecheck-client, ESLint, and hygiene are clean.
• Verified in a Code OSS dev build across classic and Modern UI at both default and compact sizes, sweeping window heights from 190px to 440px: the number of icons shown matches the space actually available at every overflow boundary, and items never overlap the global icons.

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

Benjamin Christopher Simmonds (@benibenj)

Matched files:

• src/vs/workbench/browser/parts/activitybar/activitybarPart.ts
• src/vs/workbench/browser/parts/globalCompositeBar.ts

[Copilot]

Pull request overview

Improves Activity Bar overflow calculations across classic, compact, and Modern UI layouts.

Changes:

• Derives overflow sizing from rendered item height and spacing.
• Measures global action-bar space directly.
• Adds CSS variable support and regression tests.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
activitybarPart.ts	Updates sizing and layout calculations.
globalCompositeBar.ts	Removes obsolete item-count sizing.
floatingPanels.css	Uses the shared action-gap variable.
activitybarPart.test.ts	Adds sizing regression coverage.
vscode-known-variables.json	Registers the CSS variable.

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[Mohammad javad Dianat (dianatofficial)]

Clean implementation. Types and docs are up to date.

[noreply (wenma531)]

ActivitybarPart